1. Field of the Invention
This invention generally relates to a fabrication method for a thermoelectric material. More specifically, the invention relates to a fabrication method for a nanovoid-imbedded bismuth telluride with a high figure of merit.
2. Description of the Related Art
To date, void-incorporated thermoelectric (TE) materials have been studied in only a few compound systems, such as bismuth, silicon, Si—Ge solid solutions, Al-doped SiC, strontium oxide and strontium carbonate. Si—Ge samples prepared by Pulverized and Intermixed Elements Sintering (PIES) method exhibited 30% increase in TE performance with 15-20% void fraction. Based on recent experimental research, theoretical calculations also indicated that it is possible to increase the ZT of certain materials by a factor of several times their bulk values by preparing them in 1D or 2D nanostructures. Bi—Te materials, especially with low-dimensional system, have been fabricated through solvo-thermal method (1D or 2D nanocrystals), metal-organic chemical vapor deposition (MOCVD) (2D superlattice structure), electrodeposition in porous alumina substrates (1D nanowire), and reverse micelle method (0-D quantum dots).
Typical void sizes in most of prior-art studies were in the micrometer range and no appreciable reduction in thermal conductivity was realized. Lower thermal conductivity contributes to the thermoelectric performance and in the prior-art studies, no noticeable phonon disruption was observed. Aside from theoretical predictions, there are no TE materials, based on Bi—Te, that have demonstrated such an enhancement in ZT values due to low-dimensional crystalline system. The previous studies also showed most of voids in Bi—Te film existed in an interconnected form which causes poor electron mobility, resulting in lower electrical conductivity and hence, lower thermoelectric performance.